Preparation and crystal structure of an imidazolate-bridged polynuclear complex [{Cu(im)(dien)}n][CIO4]n(dien = diethylenetriamine), and its properties in dimethyl sulphoxide solution

Abstract

The structure of [Cu(im)(dien)]ClO₄[dien = diethylenetriamine, im = Imidazolate], obtained from [Cu(Him)(dien)][ClO₄]₂(Him = imidazole) by deprotonation of the co-ordinated imidazole, was identified by X-ray crystallography. The crystals belong to the monoclinic system, space group P2₁/c, with a= 14.341(4), b= 15.473(2), c= 12.822(2)Å, β= 114.11(2)°, and Z= 8. The crystal is built up of polynuclear [Cu(im)(dien)] ClO₄ units. The geometry around each copper(II) atom is trigonal bipyramidal, comprising the tridentate diethylenetriamine ligand and two Imidazolate molecules. The copper(II) atoms are bridged by the Imidazolate rings in two alternating orientations, leading to two polynuclear units in each unit cell. In dimethyl sulphoxide solution, λ_max. for the complex is shifted by more than 30 nm to shorter wavelengths with decreasing concentration. Solution conductivity measurements did not suggest that polymeric ions were present, rather a 1:1 electrolyte. A mononuclear copper(II) complex containing Imidazolate seems to be formed under dilute conditions by dissociation of the Imidazolate bridge.